1. Field of the Invention
The present invention generally relates to methods and systems for determining one or more characteristics for defects detected on a specimen.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail.
Many inspection tools have adjustable parameters for many of the image generation elements of the tools. In this manner, the parameters for one or more elements (such as energy source(s), polarizer(s), lens(es), detector(s), and the like) can be altered depending on the type of specimen being inspected and the characteristics of the defects of interest (DOIs) on the specimen. For example, different types of specimens may have dramatically different characteristics, which can cause the same tool with the same parameters to image the specimens in extremely different ways. In addition, since different types of DOIs can have dramatically different characteristics, inspection system parameters that are suitable for detection of one type of DOI may not be suitable for detection of another type of DOI. Furthermore, different types of specimens can have different noise sources, which can interfere with detection of DOIs on the specimens in different ways.
The development of inspection tools with adjustable parameters has also led to the increasing use of inspection processes that involve scanning the specimen with more than one combination of parameters values (otherwise referred to as “modes”) such that different defect types can be detected with different modes. For example, one mode may have a greater sensitivity for detecting one type of defect while another mode may have a greater sensitivity for detecting another type of defect. Therefore, using both modes, an inspection system may be able to detect both types of defects with acceptable sensitivity.
Although using more than one mode (e.g., through a multi-channel illumination with matching multi-channel response collection) can provide advantages for defect detection, implementation has generally not been achieved in practice due to the complexity of the inspection system imaging elements and the data processing. In addition, typically in such systems, the detector output (e.g., images) that are stored for the specimen are only images produced by the mode that detected a defect (e.g., by exceeding a threshold level configured in advance by a user). In other words, when a defect is detected by one mode, the image generated for the defect by that one mode may be saved and can therefore be used post-inspection for other applications, but an image generated at the same location of the defect by another mode may not be saved if that other mode did not also detect the defect. Therefore, the image generated by the other mode that did not detect the defect may not be available for use in post-inspection defect-related functions. Furthermore, the threshold levels are separate for each mode and do not take into account the co-occurring and correlated attribute/feature values in the other modes for defect outlier detection.
Accordingly, it would be advantageous to develop systems and methods for determining one or more characteristics for defects detected on a specimen that do not have one or more of the disadvantages described above.